1. Technical Field
The present invention relates to a semiconductor integrated circuit and, more particularly, to metal interconnection structures in a semiconductor integrated circuit and methods of forming the same.
2. Description of the Related Art
As semiconductor devices having metal interconnections become more highly integrated, the width and the thickness of the metal interconnections have been reduced, resulting in a drastic increase in the electrical resistance of the metal interconnections. A copper interconnection having low resistivity is very attractive as a candidate for reducing the electrical resistance of the metal interconnections. The copper interconnection can be formed using a damascene technique. However, the copper interconnection may be easily oxidized. Thus, in the event that bonding pads of the semiconductor devices are formed from the copper layer, bonding fails may be generated during a wire bonding process for manufacturing semiconductor packages due to oxidation of the copper. Accordingly, an aluminum layer is still used in formation of the bonding pads on the copper interconnection.
FIG. 1 is a cross sectional view illustrating a method of forming conventional metal interconnections. Referring to FIG. 1, an insulating layer 30 is formed on a semiconductor substrate 10 including a lower copper interconnection 15. An upper copper interconnection 65, which is electrically connected to the lower copper interconnection 15, is formed in the insulating layer 30. The upper copper interconnection 65 is formed using a dual damascene technique. A diffusion barrier layer 75 and an aluminum pad 85, which are sequentially stacked, are formed on the upper copper interconnection 65. The diffusion barrier layer 75 and the aluminum pad 85 are formed by sequentially depositing a titanium layer, a titanium nitride layer and an aluminum layer on the insulating layer 30 and the upper copper interconnection 65 and by successively patterning the aluminum layer, the titanium layer and the titanium nitride layer using a reactive ion etching (RIE) technique.
According to the conventional art as described above, an additional process for forming the aluminum pad 85 is required after formation of the upper copper interconnection 65. Thus, the conventional art requires a complicated metallization process.
Recently, a method of replacing the upper copper interconnection 65 with an aluminum interconnection has been proposed. Such a method does not require formation of the aluminum pad 85, which simplifies the metallization process. In this case, however, copper atoms in the lower copper interconnection 15 may be diffused into the aluminum interconnection, thereby generating voids in the lower copper interconnection 15 and degrading the reliability thereof. Consequently, a method of simplifying the metallization process during formation of metal interconnections that does not result in void formation due to metal atom diffusion is desired.